Frequently, there is a need to connect a bidirectionally rotatable device with a stationary device by means of cables. Examples include radar units and robots which are being increasingly used in production lines, such as welding robots in the automotive industry.
Such robots usually perform both translatory and rotatory movements. The rotatory movements are usually effected by turning the robot base about a vertical axis of rotation, ideally at the maximum possible angle of rotation. Such robots require various electric, pneumatic, and/or hydraulic supplies. For this purpose, numerous electrical cables and fluid supply tubes are required in order to connect the bidirectionally rotating robot with stationary supply sources and signal receivers.
One problem is to take up as little space as possible for guiding the cables while simultaneously preventing excessive mechanical strain and abrasion of the cables due to the rapid to and fro movements of the robot.
One way of guiding the cables of a bidirectionally rotatable device is to use a spiral cable, the ends of which are connected to a stationary device or a rotating robot base, as, for instance, described in DE-37 15 118 C2. In this case, a sturdy spiral and a stable guiding system are provided by an elastic outer strand which creates pre-tension in the unwinding direction and an elastic inner strand which creates pre-tension in the winding up direction. The outer and the inner strand are attached to the supply line over the entire length of the spiral or at attachment spots provided at pre-determined intervals. This solution works fairly well, but assembly costs are high and a relatively long cable is required to realize a certain maximum angle of rotation.
An alternative would be a drag chain as disclosed in DE-PS 23 62 463, but placing it on its side, as shown on page 15.2. of a brochure of the company "KABELSCHLEPP" relating to their "energy guiding device, Type 210." The construction provides for a rotatable body and a concentric, stationary housing, leaving open a ring-shaped recess for accommodating the drag chain. The chain is layed in a U-shaped loop into the ring-shaped recess at one side of the axis of rotation, and the free ends of both loop strands are attached to the rotatable body/stationary housing. Depending on the direction of rotation of the rotatable body, the drag chain either contacts the outer circumference of the rotatable body or the inner circumference of the stationary housing. The maximum rotation angle feasible with this construction is approximately 350.degree..
The drag chain is formed by two link chains the links of which are arranged on top of one another and are connected by a bar incorporating openings in which the cables which are arranged on top of one another are guided by the drag chain. The chain links of the lower link chain are provided with carrier rollers with which the chain on its support is carried such as to allow displacement of the chain. Lateral guide rollers project from the links of the upper chain. These rollers run on the outer circumference of the rotatable body/inner circumference of the housing.
The maximum possible angle of rotation which may be achieved using the known drag chain is not sufficient for many applications.
Since the rotatable body of most robots has to be supplied by numerous cables, which are placed on top of one another both in the spiral cable and the drag chain construction, the construction becomes very high and requires a lot of space.
There is a need for an assembly for guiding cables, which requires less space and allows for a greater angle of rotation, while requiring a shorter length of cable.